Impulsive-antisocial traits are a significant predictor of aggression, criminal behavior, and recidivism. However, the neurobiological mechanisms driving variability in this dimension of personality are poorly understood. Given prior work suggesting enhanced reward-related striatal dopamine transmission in impulsive-antisocial community volunteers (Buckholtz et. al. 2010), we predicted that such traits would be linked to the aberrant development of corticostriatal circuits. To test this hypothesis,we analyzed brain morphometry within a sample of incarcerated criminal offenders who received an extensive clinical assessment following structural MRI via mobile 1.5T MR scanner.49 male inmates (age 20-45; mean = 31) at two medium-security state prisons completed an extensive clinical assessment and and high-resolution T1-weighted structural MR. Morphometric analyses were completed using Freesurfer, yielding measurements of both cortical thickness and subcortical volume. Consistent with our prediction, variation in corticostriatal gray matter was significantly predicted by variation in impulsive-antisocial behavior. Specifically,higher levels of impulsive-antisociality were associated with higher gray striatal gray matter volume, particularly in the nucleus accumbens and caudate head. By contrast we observed lower cortical thickness in lateral prefrontal cortex in impulsive-antisocial individuals, with the most pronounced effects in the inferior frontal gyrus and dorsal cingulate. These effects were observed even after controlling for variation in age and substance abuse history. As a complimentary analysis,we used voxel-based morphometry (VBM) to measure the effects of variability in impulsive-antisocial behavior on gray matter concentration across the whole brain. VBM findings largely converged with Freesurfer analyses, pointing to increased striatal gray matter in the context of reduced prefrontal structure. Of note, similar effects for psychopathy (measured via PCL-R) were observed in the striatum, with psychopathic offenders showing significantly greater gray matter volume in the striatum compared to non-psychopathic offenders. However, unlike impulsive-antisociality, we did not find consistent evidence for differences in prefrontal cortical thickness or volume driven by PCL-R scores. These data accord with prior work showing enhanced striatal reactivity in impulsive-antisocial individuals and provide a structural foundation for such effects. Further, we show a structural dissociation between impulsive-antisocial behavior ("externalizing") and psychopathy within corticostriatal circuitry.